The present invention relates to an apparatus comprising an inflatable vehicle occupant protection device, and particularly relates to a gas generating composition for providing inflation gas for inflating an inflatable vehicle occupant protection device.
An inflator for inflating an inflatable vehicle occupant protection device, such as an air bag, contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated so as to ignite the body of gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
Azide based gas generating compositions for generating gas to inflate an inflatable vehicle occupant protection device have the advantage that they produce gas at relatively low gas temperatures, in the range of 1100 K to 1500 K.
Non-azide based gas generating compositions, in contrast, typically produce gas at temperatures well above the cooler burning azide based gas generating compositions. While these hot burning gas generating compositions potentially are thermodynamically efficient, they present difficult heat management problems. For instance, it may be necessary, because of the high temperatures, to manufacture certain components of the vehicle occupant protection device of expensive materials resistant to the high temperature gas which is generated.
In addition, the non-azide based gas generating compositions may produce toxic reaction products which are in a vapor phase at the high temperature of combustion and thus difficult to filter. To reduce the production of toxic reaction products and achieve other advantages, it is generally desirable to achieve an oxygen balance in the combustion reaction.
A further problem with some non-azide based gas generating compositions is that the fuel molecules in the compositions may include relatively large numbers of hydrogen atoms. This can lead to the production of water and potentially steam during combustion. It is desirable to have a low water content in the exhaust gas.
The present invention is an apparatus which comprises an inflatable vehicle occupant protection device and a gas generating composition which when ignited produces gas to inflate the inflatable vehicle occupant protection device. The gas generating composition comprises an oxidizer and a fuel. The oxidizer is an inorganic salt. The fuel is a tetrazine. Preferred fuels are selected from the group consisting of 3-R1-6-R2-1,2,4,5-tetrazine, 3-R1-6-R2-1,2,4,5-tetrazine-1,4-dioxide, 1,2,3,4-tetrazine, 3-R1-6-R2-3,6-dihydro-1,2,4,5-tetrazine, and 3-R1-6-R2-1,2-dihydro-1,2,4,5-tetrazine. R1 and R2 are non-metallic substituents bonded to the carbon atoms at the 3 and 6 positions, respectively, of the tetrazine ring, and selected from the group consisting of: hydro; amino and derivatives thereof; tetrazolyl and derivatives thereof; triazolyl and derivatives thereof; azido and derivatives thereof; carboxyl and derivatives thereof; and mixtures thereof. R1 and R2 can be the same non-metallic substituent or different non-metallic substituents.
The tetrazine and tetrazine derivative molecules contain fewer carbon and/or hydrogen atoms than conventional fuel components, and thus release less heat on combustion. In addition, they can be oxygen balanced to the production of carbon dioxide with the use of less oxidizer. Further, the presence of fewer hydrogen atoms in the fuel molecule results in a lower water content in the exhaust gas which is produced.